MEPS 286:69-79 (2005)  -  doi:10.3354/meps286069

ABSTRACT: The importance of organic matter produced in seagrass meadows (seagrass and epiphytic algae) to the nutrition of a valuable fisheries species (yellowfin whiting Sillago schomburgkii Peters) occurring over unvegetated mudflats was measured using the isotopic composition (δ¹³C, δ¹⁵N) of fish, their polychaete prey, and available autotrophic sources at several locations in southern Australia during 2 periods (summer, winter). Values for δ¹³C and δ¹⁵N for autotrophs and fishes varied little between seasons. Sources could be separated into 3 groups based on δ¹³C: seagrass and epiphytes (mean δ¹³C = -10.5‰), benthic microalgae and macroalgae (-19.5‰), and saltmarsh and mangroves (-26.5‰). Values of δ¹⁵N for the sources were 2 to 5‰. Values of δ¹³C for fish (-13.3‰) corresponded with those of their polychaete prey (-12.5‰) and ultimately with those of seagrass and epiphytes. Values of δ¹⁵N were 5 to 6‰ more enriched than sources. Modelling of feasible source mixtures showed that seagrass and epiphytes were the most important contributors to the nutrition of fish, but their relative importance varied between seasons. The median contribution by other sources was <10%. Spatial analyses showed that saltmarsh plants contributed significantly to the variability in S. schomburgkii nutrition among locations, while macroalgae contributed in summer. The similarity in δ¹³C values of polychaetes and S. schomburgkii is consistent with source material from a subtidal habitat being incorporated into food webs supporting a fisheries species in adjacent intertidal habitats via a largely sedentary intermediary.

KEY WORDS: Posidonia · Mangrove · Saltmarsh · Algae · Sillaginidae · Diet · Trophic ecology